From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 28EA3C433DB for ; Fri, 26 Feb 2021 05:33:56 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B511864E60 for ; Fri, 26 Feb 2021 05:33:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B511864E60 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=X4aS/oSp5HvMAUfDIyQdpQSa+Lqs1Z+TrtrbAAn3Tgg=; b=K17LzrXeBB/Cw40niVrx9wn0k ETjf+qRQoLkQD/1By7XfyaOQsE8r0R5TY7v/klmC3Kqyure2Zm5Y/RgPIEOxZEo0F3KvBh4ZWK9WH rXsVKdpnhhpzAhZwCowrYIVfRbyg1vK9gAP0nBKBQGf1myQAM9IPBHfxxfKKIAM4W0SxyU3E6EBj6 en+0nQQey0pBOL5a6NpgGpfPKCjUI8HjmuT07hat8jtS1fJlO/4G3MmYKrZYb2mcMr9HbhC+2X0GG IaAAajbpsiSx7EhpEadO34wE4eBO6bbsV1GIahLCUAO9DTj3UUjkdZnmf3pxG/ueroixOGT9pfS6h ybsIjZitw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1lFVjo-0000Mz-UJ; Fri, 26 Feb 2021 05:32:28 +0000 Received: from casper.infradead.org ([2001:8b0:10b:1236::1]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1lFVjn-0000Ml-Gr; Fri, 26 Feb 2021 05:32:27 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=rWddWXnuro4YAoJY8JcUhOg9+DBTrAAV7EgLMgansOs=; b=Y95JvHz+p/fgRuSqZdUJ6kTozG 0hAoFtiyNg4giHk7sA+bUreJm0TfS3bLevc6PdklG1y06IzBDHblgOs5KDo9/3NWCY7NuMA/7UByg 9jrDHwNwr5X1zHL8GYCCj0qcmzuCZ5LuVSQIWYroEgW1XQmEOlqVfUgYZRdlAspXhZcYl7YsK+cC8 BCoG5w3WO3JuUlZ42r1a7m+lvxdVhuZk0p4FfsKRNYqw4tXn5We8K20zdsnscKzt8F/YATHIqQgHr ebQ03kMaxevLZc0Q8VZCIhTZKr4mmk0mW9HRB3r69f6tERAcAurrZcGA/SC0wowDiJtUBHY8Zgqd6 bX7rKyag==; Received: from hch by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lFVjj-00Bb9c-6O; Fri, 26 Feb 2021 05:32:23 +0000 Date: Fri, 26 Feb 2021 05:32:23 +0000 From: Christoph Hellwig To: Nicolas Saenz Julienne Subject: Re: RPi4 can't deal with 64 bit PCI accesses Message-ID: <20210226053223.GA2763268@infradead.org> References: <2220c875-f327-586c-79c7-eadff87e4b4d@arm.com> <6088038a-2366-2f63-0678-c65a0d2efabd@gmail.com> <20210224202538.GA2346950@infradead.org> <0142a12e-8637-5d8e-673a-20953807d0d4@gmail.com> <0e52b124-e5a8-cdea-9f15-11be8c20af2a@baylibre.com> <0cca5246-065b-b52e-7005-b1b5229922a7@arm.com> <01091991523dac4c0c7e40f40e95c887af84f560.camel@suse.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <01091991523dac4c0c7e40f40e95c887af84f560.camel@suse.de> X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: devicetree , Florian Fainelli , Rob Herring , linux-pci , Neil Armstrong , Christoph Hellwig , Bjorn Helgaas , linux-rpi-kernel , bcm-kernel-feedback-list , Robin Murphy , linux-arm-kernel , Robin Murphy Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Feb 25, 2021 at 12:35:27PM +0100, Nicolas Saenz Julienne wrote: > Yes, that's what I had in mind myself. All in all, why penalize the rest of > busses in the system. What I'm planning is to introduce a '64bit-mmio-broken' > DT property that'll utimately live somwhere in 'struct device.' > > WRT why not defaulting to 32-bit accesses for distro images if they support > RPi4. My *un-educated* guess is that, the performance penalty of checking for a > device flag is (way) lower than having to resort to two distinct write > operations with their assorted memory barriers. I'm sure you can > comment/correct me here. Various high performance devices rely on the fact that 64-bit MMIO writes are atomic, and will have to use an extra lock and/or an entirely different programming model if they are not supported. If that is not the case just using 32-bit accesses always is certainly easier, that's what we did for the slow-path only 64-bit registers in NVMe. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel